The present invention relates generally to metal deforming and specifically to an apparatus and a method for melting granulated metal and/or high-grade crystalline ore.
The present invention has evolved because of the environmental and economic rewards achieved by recycling metal, particularly metals which can be used as conductors in the fabrication of wire and cable that is already in the form of wire, cable or electronic apparatus. Scrap such as scrap wire, scrap cable and scrap electronic apparatus is in demand because of its relative purity.
Metal has been recovered from scrap insulated wire and cable by various insulation stripping and breaking methods disclosed in U.S. Pat. Nos. 3,309,947, 3,724,189, 3,858,776, 3,936,922, 3,977,277 and 4,083,096. U.S. Pat. No. 3,975,208 discloses a method of selectively recovering vinyl halide insulation and metal from scrap insulated wire and cable by the use of chemical solvent. These methods of metal recovery are inflexible because each method can recover metal from limited types of cable and wire. For instance, insulation stripping or breaking of short irregular pieces of scrap wire and cable is not economically feasible and the chemical solvent method is limited to cable and wire with a specific type of insulation. This inflexibility combined with an increasing variety of scrap wire and cable has forced many portions of the industry to chop or granulate the scrap and to separate various sizes, lengths and compositions of the chopped scrap into particles of insulation and particles of metal, by a mechanical separation process thereby producing a particulate feed material of substantially high purity.
Once isolated, metal granules or particles must be melted and refined for recycling into new products. Granulated metal recovered by the granulator process and other types of granulated metal such as shavings, borings, chips and turnings as well as high-grade crystalline ore are normally melted in reverberatory smelting furnaces such as those disclosed in U.S. Pat. Nos. 2,436,124, 3,664,828 and 3,614,079 because of processing difficulties which were encountered when such feed material was processed in vertical shaft-type furnaces. Thus, until the present invention, the options for use in melting granulated metal were restricted to either high energy consuming reverberatory furnaces or mixing very small amounts of granulated metal with large metal pieces in a conventional vertical shaft furnace.
Vertical shaft melting and refining furnaces are well known in the metal melting art. One of the most severe problems experienced with the melting of granulated scrap in prior art shaft furnaces is the formation of a cold state semi-solid mass of metal on the hearth which clogs the tap hole and blocks the burners. In a shaft furnace, the charge must progress down the shaft at a rate slow enough to allow the metal to melt and be carried away through the tap hole because metal settling through the shaft too rapidly will not melt but will instead reach the hearth in the cold state and form a semi-solid mass on the hearth with the unwanted results described above. U.S. Pat. No. 2,283,163 discloses a vertical shaft furnace for melting metal scrap which has an enlarged lower portion for collecting excess heat for independent transfer to other areas of the furnace and where the actual melting of the scrap metal takes place. U.S. Pat. No. 2,283,163 further teaches that during preheating of the scrap charge in the shaft of the furnace, care must be taken to prevent the charge metal from sticking together to prevent clogging of the furnace shaft which the inventor of U.S. Pat. No. 2,283,163 says will happen if substantial quantities of coke or ore are not included in the charge. Controlled combustion in a gas tight vertical shaft furnace to eliminate unwanted oxygen is disclosed in U.S. Pat. No. 3,199,977. Other vertical shaft furnaces are disclosed in U.S. Pat. Nos. 3,715,203 and 3,788,623; but like the furnace of U.S. Pat. No. 2,283,163, none of these furnaces can melt large amounts of granulated scrap metal or high-grade crystalline ore which has not been mixed with other elements such as coke. The present invention solves this problem by providing a vertical shaft melting furnace capable of melting scrap charges containing substantial quantities of copper fines as small as 300 without the intentional blending of fluxes or fuels in such charges as well as charges consisting entirely of nugget sized copper particles and mixtures thereof.